About Tourmaline Breccia Pipes

Copper-bearing tourmaline pipes are a distinctive class of intrusion-related breccias which vary considerably in size and metal content. They are speculated to be derived from granitic to granodioritic magmas initiated at deeper crustal levels than generally much larger copper-bearing pipes associated with porphyry copper deposits. As a consequence, intrusion related pipes tend to increase in size with depth, in contrast with porphyry-related examples which typically flare upwards due to much less lithostatic pressure exerted by the host wallrocks. Both deposit types can have vertical dimensions exceeding one kilometer. The common presence of decompressive shock textures and shingle breccias provide further evidence for deeper emplacement of the intrusion-related pipes. In terms of mineralization, complex multi-element assemblages (Cu, Mo, Au, Ag, As, Bi, Wo3, Pb and Zn) typically characterize the deeper smaller pipes in contrast to the generally simple Cu-Mo association observed in porphyry environments. The highest metal concentration is normally found near the inside margins of the tourmaline pipes, and especially in the non-porphyry derived examples where there is normally intense development of shingle breccias.